Probing Dark Matter Spikes via Gravitational Waves of Extreme Mass Ratio Inspirals

TL;DR

This paper explores how dark matter spikes around black holes can significantly alter gravitational wave signals from extreme mass ratio inspirals, affecting their detectability by future space-based GW detectors.

Contribution

It demonstrates that dark matter spikes can modify EMRI gravitational waveforms, influencing signal strength and detection prospects with upcoming GW observatories.

Findings

Dark matter spikes can suppress low-frequency GW signals.

Dark matter spikes can enhance GW signals at higher frequencies.

Detection sensitivity of EMRIs is affected by dark matter density.

Abstract

The exact properties of dark matter remain largely unknown despite the accumulating evidence. If dark matter is composed of weakly interacting massive particles, it would be accreted by the black hole in the galactic center and form a dense, cuspy spike. Dynamical friction from this spike may have observable effects in a binary system. We consider extreme-mass-ratio inspiral (EMRI) binaries comprising massive black holes harbored in dark matter spikes and stellar mass objects in elliptic orbits. We find that the gravitational-wave waveforms in the frequency domain can be substantially modified. In particular, we show that dark matter can suppress the characteristic strain of a gravitational wave at low frequency but enhance it at a higher domain. These effects are more dramatic as the dark matter density increases. The results indicate that the signal-to-noise ratio of EMRIs can be strongly reduced near $10^{-3}\sim 0.3$~Hz but enhanced near $1.0$~Hz with a higher sensitivity, which can be probed via the future space-borne gravitational-wave (GW) detectors, LISA and TAIJI. The findings will have important impacts on the detection and parameter inference of EMRIs.